The present invention relates to a baud rate mixing transmission system for transmitting data signals at a plurality of different transmission rates (baud rates) at time intervals, and receiving transmitted data signals in accordance with corresponding baud rates.
As the first apparatus for receiving data signals transmitted at a plurality of different baud rates at time intervals, a data reception apparatus is disclosed in, e.g. Japanese Patent Laid-Open No. 5-83328. This first apparatus includes a generating means for generating clock signals corresponding to a plurality of baud rates such as 200 bps, 600 pbs, and 1,200 pbs. When a data signal is to be received, the transmitted data signal is sampled to discriminate a synchronization pattern, and a baud rate is calculated from the discriminated synchronization pattern. A corresponding reception clock signal is selected from the generating means on the basis of this calculation result, and subsequent data reception is performed on the basis of the selected reception clock signal
The second apparatus disclosed in Japanese Patent Laid-Open No. 1-238338 includes two types of data interval detecting circuits for detecting the specific baud rates of data signals from the transmitted data signals, and a count circuit for sampling input data with an external clock signal. Detection results obtained by the respective detecting circuits are supplied, as control signals, to gate circuits arranged for the respective baud rates. A data signal having a desired baud rate is output from the output terminal of a gate circuit corresponding to the desired baud rate.
In the first apparatus described above, since a specific timing at which the baud rate of a data signal transmitted from the transmission side changes is unknown on the reception side, a baud rate is determined by using a synchronization pattern. In the second apparatus, when a data signal transmitted from the transmission side is to be received, a data interval is set for the data signal to determine a specific baud rate.
In both the apparatuses, therefore, when a data signal transmitted from the transmission side is to be received on the reception side, detection processing must be performed while expecting all baud rate values from the data signal. In the first apparatus, in particular, baud rate detection processing is complicated. In the second apparatus, a complicated, large-size detection circuit is required.
Furthermore in both the apparatuses since a baud rate is directly detected from a data signal transmitted from the transmission side, the processing time between the instant at which a baud rate changes and the instant at which this baud rate is detected is required. During such a detection processing time, therefore, received data cannot be properly detected on the reception side. Consequently, the received data during this time is lost.